Method of topology-selective film formation of silicon oxide

ABSTRACT

A method for forming a dielectric film containing a Si—O bond a trench formed in an upper surface of a substrate, includes: designing a topology of a final dielectric film containing a Si—O bond formed in the trench by preselecting a target portion to be selectively removed relative to a non-target portion of an initial dielectric film resulting in the final dielectric film; conformally depositing the initial dielectric film on the upper surface and in the trench; and relatively increasing an amount of impurities contained in the target portion of the initial dielectric film relative to an amount of impurities contained in the non-target portion of the initial dielectric film to obtain a treated dielectric film, thereby giving the target portion and the non-target portion different chemical resistance properties when subjected to etching.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/800,210 filed on Feb. 1, 2019, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND Field of the Invention

The present invention relates generally to a method for forming a dielectric film containing a Si—O bond on a step formed on a surface of a substrate, particularly, a method of topology-selective film formation of silicon oxide.

Related Art

Atomic layer deposition (ALD) is characterized not only by excellent controllability over film thickness and excellent uniformity of film, but also by being capable of depositing a film uniformly covering a three-dimensional structure, and accordingly, ALD has been recognized to be a very important deposition method in the semiconductor industry. On the other hand, in a certain semiconductor device-manufacturing process, there is demand for non-uniform formation of film, e.g., in gate spacers wherein only sidewall portions of film deposited in trenches are selectively left in certain areas, and in that case, film deposition by ALD is used in combination with anisotropic dry etching to form a desired pattern. However, because it is difficult to determine the end point of dry etching, there is a concern of over-etching where an underlying layer is damaged.

As such technology of patterning, it is known that first a SiN film is deposited on a patterned surface of a substrate under certain conditions such that a wet etch rate of a horizontal portion and that of a vertical portion of the pattern are different, followed by wet etching, thereby leaving selectively only either a sidewall portion of the pattern or a horizontal portion of the pattern (as disclosed in e.g., U.S. patent application publication No. 2017/0243734, the disclosure of which is incorporated by reference in its entirety as applicable to certain embodiments disclosed herein). That technology may be referred to as topology-selective film formation of SiN (“TS-SiN”). In the above, since wet etching, not dry etching, is used to selectively remove only either a vertical or horizontal portion of the pattern, it is possible to set high wet-etching selectivity of the pattern relative to the underlying film, and to realize an advantage that uniformity of etching need not be considered. In TS—SiN, the high wet-etching selectivity can be obtained by increasing RF power; however, such conditions do not work on SiO film to render similar high wet-etching selectivity. Thus, although there is high demand for topology-selective film formation of SiO (“TS—SiO”) in the semiconductor industry, TS—SiO has not been successfully realized.

Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.

SUMMARY

In some embodiments, by introducing impurities to a SiO₂ film deposited in a pattern on a substrate by plasma-enhanced ALD (PEALD), the wet etch rate of the film for HF (hydrofluoric acid) is manipulated, thereby selectively leaving substantially only or predominantly either a vertical or horizontal portion of the pattern formed on the substrate. In some embodiments, halogen atoms and/or carbon atoms are used as impurities. In some embodiments, by topologically manipulating the concentration of impurities present in a patterned surface of a substrate, the distribution of impurities is adjusted such that the impurities are left selectively in a vertical portion of the pattern or the impurities are anisotropically introduced selectively in a horizontal portion of the pattern, thereby realizing topology-selective film formation. In some embodiments, the impurities contained in the SiO₂ film may originate in or be derived from a precursor and/or may subsequently be introduced to a surface of the SiO₂ film through an additional film formation or additional surface treatment using a non-silicon gas. In some embodiments, the subsequent introduction of impurities is accomplished by PECVD or PEALD, wherein the subsequent introduction cycle is performed after every one cycle of deposition or multiple cycles of deposition.

In particular, by way of examples, TS—SiO can be conducted as follows:

1) First, deposit a SiO₂ film using a precursor containing carbon and/or halogen; and then, expose the SiO₂ film to a plasma generated at relatively low pressure and relatively high RF power, thereby forming an anisotropic distribution of impurities in the SiO₂ film, wherein impurities contained in the SiO₂ film are selectively removed significantly more from a horizontal portion of a pattern than from a vertical portion of the pattern. The impurity removal cycle is performed after every one cycle of deposition or multiple cycles of deposition.

2) First, deposit a SiO₂ film; second, adsorb impurities to a surface of the SiO₂ film by exposing the surface of the SiO₂ film to a non-silicon gas containing carbon and/or halogen as impurities; and then, expose the impurity-adsorbed SiO₂ film to a plasma generated at relatively low pressure and relatively high RF power, thereby forming an anisotropic distribution of impurities in the SiO₂ film, wherein impurities are selectively introduced significantly more to a vertical portion of a pattern than to a horizontal portion of the pattern. The impurity addition cycle is performed after every one cycle of deposition or multiple cycles of deposition. In the above, for depositing the SiO₂ film, any suitable precursor containing silicon can be used, regardless of whether the precursor contains carbon and/or halogen.

3) After step 1) or 2) above, subject the SiO₂ film to wet etching using dHF, thereby selectively removing a portion of the pattern which contains more impurities than does the remaining portion of the pattern, whereby TS—SiO can be accomplished wherein substantially only or predominantly either a vertical or horizontal portion of the pattern can selectively be removed.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a protective film usable in an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 is a flowchart illustrating steps of topology-selective film formation according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating steps of topology-selective film formation according to another embodiment of the present invention.

FIG. 4 is a flowchart illustrating steps of topology-selective film formation according to still another embodiment of the present invention.

FIG. 5 illustrates schematic cross-sectional views showing processes of topology-selective film formation according to different embodiments of the present invention ((a) and (b) represent one embodiment, whereas (a) and (c) represent the other embodiment).

FIG. 6 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of a silicon oxide film as deposited in (a), a silicon oxide film after dHF etching without reforming treatment in (b), and a silicon oxide film after dHF etching upon reforming treatment in (c) according to an embodiment of the present invention.

FIG. 7 is a graph showing the relationship between treatment pressure [kPa] and wet etch rate (“WERR. Tox”: wet etch rate relative to thermal oxide) of a film formed on a top surface (a blanket film) according to embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a precursor gas and an additive gas. The precursor gas and the additive gas are typically introduced as a mixed gas or separately to a reaction space. The precursor gas can be introduced with a carrier gas such as a noble gas. The additive gas may be comprised of, consist essentially of, or consist of a reactant gas and a dilution gas such as a noble gas. The reactant gas and the dilution gas may be introduced as a mixed gas or separately to the reaction space. A precursor may be comprised of two or more precursors, and a reactant gas may be comprised of two or more reactant gases. The precursor is a gas chemisorbed on a substrate and typically containing a metalloid or metal element which constitutes a main structure of a matrix of a dielectric film, and the reactant gas for deposition is a gas reacting with the precursor chemisorbed on a substrate when the gas is excited to fix an atomic layer or monolayer on the substrate. “Chemisorption” refers to chemical saturation adsorption. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a noble gas. In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers.

In this disclosure, “containing a Si—O bond” may refer to being characterized by a Si—O bond or Si—O bonds, having a main skeleton substantially constituted by a Si—O bond or Si—O bonds, and/or having a substituent substantially constituted by a Si—O bond or Si—O bonds. A dielectric film containing a Si—O bond includes, but is not limited to, a SiO film, a SiOC film, and a SiON film, which have a dielectric constant of about 2 to 10, typically about 4 to 8.

In this disclosure, “annealing” refers to a process during which a material is treated to become its stable form, e.g., a terminal group (such as an alcohol group and hydroxyl group) present in a component is replaced with a more stable group (such as a Si-Me group) and/or forms a more stable form (such as a Si—O bond), typically causing densification of a film.

Further, in this disclosure, the article “a” or “an” refers to a species or a genus including multiple species unless specified otherwise. The terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. Also, in this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

Additionally, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments. However, the present invention is not limited to the preferred embodiments.

Some embodiments provide a method for forming a dielectric film containing a Si—O bond on a step formed on a surface of a substrate, comprising processes of: (i) designing a topology of a final dielectric film containing a Si—O bond formed on the step by preselecting a target portion to be selectively removed with reference to a non-target portion of an initial dielectric film resulting in the final dielectric film, said target portion being a top/bottom portion of the initial dielectric film formed on a top surface and a bottom surface of the step or a sidewall portion of the initial dielectric film formed on a sidewall of the step; (ii) conformally depositing the initial dielectric film on the top surface, the bottom surface, and the sidewall of the step; (iii) relatively increasing an amount of impurities contained in the target portion of the initial dielectric film relative to an amount of impurities contained in the non-target portion of the initial dielectric film to obtain a treated dielectric film, thereby giving the target portion and the non-target portion different chemical resistance properties when subjected to etching; and (iv) etching the treated dielectric film to obtain the final dielectric film. As a result, substantially only or predominantly either a vertical or horizontal portion of the pattern can be removed, thereby accomplishing topology-selective film formation of SiO. In this disclosure, the term “substantially” or the like may refer to ample, considerable, or material quantity, size, time, or space (e.g., at least 70%, 80%, 90%, or 95% relative to the total or referenced value in a concerned portion) recognized by a skilled artisan in the art to be sufficient for the intended purposes or functions. For example, the term “substantially only” or the like may refer to a configuration where a ratio of a target portion to a remaining portion is at least 70/30, 80/20, 90/10, or 95/5 in thickness.

In this disclosure, the term “step” refers to any concave and/or convex pattern, including but not limited to a trench, formed in a substrate, and in some embodiments, the trench may have a width of about 10 to about 50 nm (typically about 15 to about 30 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is about 10 to about 50 nm), a depth of about 30 to about 200 nm (typically about 50 to about 150 nm), and an aspect ratio of about 3 to about 20 (typically about 3 to about 10). In some embodiments, the silicon oxide film deposited on the upper surface and in the trench of the substrate has a conformality of about 70% to about 100% (typically about 80% or higher, more typically about 90% or higher) wherein the “conformality” is determined by comparing film thickness deposited at some point (typically a middle point in a cross sectional view) on a sidewall or on a bottom of a recess to film thickness deposited on a flat surface just outside the recess.

In some embodiments, the impurities include carbon and/or halogen.

In some embodiments, in process (i), the sidewall portion is preselected as the target portion, and in process (ii), the initial dielectric film is deposited using a silicon-containing precursor further containing carbon and/or halogen, and in process (iii), the amount of impurities contained in the target portion is relatively increased by decreasing the amount of impurities contained in the non-target portion of the initial dielectric film by anisotropic bombardment of a plasma excited by applying RF power between two electrodes between which the substrate is placed in parallel to the two electrodes. This embodiment may be referred to as “top/bottom-thick TS—SiO by area-selective removal of impurities.” In this embodiment, by anisotropic ion bombardment by a plasma, a horizontal portion of the film is predominantly attached, and as a result, the horizontal portion becomes densified and impurities are dissociated or separated and removed selectively from the horizontal portion relative to a vertical portion of the film, thereby area-selectively increasing chemical resistance in the horizontal portion and decreasing its wet etch rate (i.e., substantially only or predominantly leaving the top/bottom portion of the film).

In some embodiments, in the top/bottom-thick TS—SiO by area-selective removal of impurities, the silicon-containing precursor is selected from the group consisting of Si₂R_(y)Cl_(6-y) wherein y is an integer of 0 to 5, and SiR_(x)Cl_(4-x) wherein R is H or an alkyl group, and x is an integer of 0 to 3. For example, such precursors include, but are not limited to, Si₂Cl₆, SiCl₄, and/or Si₂Cl₂(CH₃)₄. Further, in some embodiments, the RF power is 600 W to 1,000 W as calculated for a 300-mm wafer, and is applied under a pressure of 1 to 100 Pa.

In some embodiments, in process (i), the top/bottom portion is preselected as the target portion, and in process (iii), the amount of impurities contained in the target portion is relatively increased by increasing the amount of impurities contained in the target portion of the initial dielectric film by (iiia) adsorbing a non-silicon gas containing carbon and/or halogen on the entire exposed surface of the initial dielectric film, and (iiib) subjecting the non-silicon gas-adsorbed surface to anisotropic bombardment of a plasma excited by applying RF power between two electrodes between which the substrate is placed in parallel to the two electrodes. This embodiment may be referred to as “sidewall-thick TS—SiO by area-selective incorporation of impurities.” In this embodiment, by introducing impurities to a surface of the film, followed by anisotropic ion bombardment by a plasma, a horizontal portion of the film is predominantly attached, and as a result, the horizontal portion becomes densified and impurities are incorporated and introduced selectively to the horizontal portion relative to a vertical portion of the film, thereby area-selectively decreasing chemical resistance in the horizontal portion and increasing its wet etch rate (i.e., substantially only or predominantly leaving the sidewall portion of the film).

In some embodiments, in process (i), the top/bottom portion is preselected as the target portion, and in process (iii), the amount of impurities contained in the target portion is relatively increased by increasing the amount of impurities contained in the target portion of the initial dielectric film by (iiic) subjecting the initial dielectric film to anisotropic bombardment of a plasma excited by applying RF power, in the presence of a non-silicon gas containing carbon and/or halogen, between two electrodes between which the substrate is placed in parallel to the two electrodes. The above is also a sidewall-thick TS—SiO by area-selective incorporation of impurities. In the above, instead of processes (iiia) and (iiib), process (iiic) is conducted where impurities are included in a plasma gas, rather than adsorbing impurities onto a surface of the film, followed by plasma exposure.

In some embodiments, since in the sidewall-thick TS—SiO by area-selective incorporation of impurities, non-silicon gas is used to introduce impurities to the film, the precursor itself need not contain impurities and can be those conventionally used. For example, such precursors include, but are not limited to, NxHy (x and y are integers other than zero), NxCyHz (x, y, and z are integers other than zero), and/or N₂. In some embodiments, the precursor does not contain carbon or halogen.

In some embodiments, in the sidewall-thick TS—SiO by area-selective incorporation of impurities, the non-silicon gas is selected from the group consisting of hydrocarbon gas, halogen gas, and halogenated gas. For example, such non-silicon gases include, but are not limited to, CH₄, C₂H₆, Cl₂, Br₂, CCl₄, etc., or other hydrocarbon, halogen, and halogenated gases which typically are liquid and have a vapor pressure of 10 Torr or higher. Further, in some embodiments, the RF power is 600 W to 1,000 W as calculated for a 300-mm wafer, and is applied under a pressure of 1 to 100 Pa.

In some embodiments, in process (ii), the initial dielectric film is deposited by plasma-enhanced ALD or thermal ALD.

In some embodiments, in process (iv), the etching is wet-etching using dHF. In some embodiments, the concentration of HF is approximately 0.1%.

The present invention will be explained in detail with reference to preferred embodiments illustrated in the drawings. However, the present invention is not intended to be limited to these embodiments.

FIG. 2 is a flowchart illustrating processes of topology-selective film formation of SiO (TS—SiO) according to an embodiment of the present invention, which is the top/bottom-thick TS—SiO by area-selective removal of impurities. In step S1, a SiO film is deposited on a substrate having trenches using a precursor containing impurities. The deposition can be done by any suitable method such as PEALD, thermal ALD, cyclic CVD, or PECVD. In step S2, the deposited film is exposed to a noble gas plasma at relatively low pressure and relatively high RF power so that impurities contained in a horizontal portion of the film are predominantly or sufficiently removed as compared with those contained in a vertical portion of the film. Step S1 and step S2 are continuously conducted without interruption (without breaking a vacuum) so that no or little impurities are incorporated or adsorbed onto a surface of the deposited film between step S1 and step S2 from the atmosphere surrounding the substrate. When step S1 is cyclic deposition, step S2 can be conducted after every one cycle of the cyclic deposition (depositing a monolayer) or after every two or more cycles of the cyclic deposition (depositing a laminate of monolayers). However, the thickness of the film obtained in step S1 should not be more than that which ion bombardment by a plasma cannot penetrate in step S2. A set of step S1 and step S2 can be repeated multiple times until a desired thickness of the film is obtained. In some embodiments, the thickness of the deposited film on the top surface is about 3 nm to about 50 nm, typically about 10 nm to about 30 nm, depending on the intended purposes or use of the deposited film. In some embodiments, step S2 can be conducted under the conditions shown in Table 1 below.

TABLE 1 (numbers are approximate) Conditions for Post-Deposition Treatment Substrate temperature 50 to 600° C. (preferably 200 to 500° C.) Pressure 1 to 500 Pa (preferably 1 to 300 Pa, more preferably 1 to 100 Pa), depending on RF power Noble gas Ar, He Flow rate of noble gas 100 to 5000 sccm (preferably 500 to 3000 (continuous) sccm) RF power (13.56 MHz) 500 to 3000 W (preferably 600 to 1000 W, for a 300-mm wafer more preferably 600 to 900 W), depending on the pressure Duration of RF power 0.5 to 5 sec. (preferably 1 to 3 sec.) application Distance between 3 to 20 mm (preferably 5 to 15 mm) electrodes Duration 1 to 300 sec. (preferably 30 to 90 sec.), depending on the thickness of the film

“W” can be converted to “W/cm²” per area of a substrate, and the converted value in W/cm² can be applied to a different size of substrate such as a 200-mm substrate and a 450-mm substrate. Suitable RF power applied to the reaction space for post-deposition treatment is determined depending on the pressure of the reaction space, since the effect of the treatment depends on the ion energy of the plasma. Thus, for example, typically, the pressure is about 400 Pa or less (preferably about 100 Pa or less), and RF power is about 600 W or higher (e.g., at 400 Pa), wherein the lower the pressure, the lower the RF power can be applied. Since the deposition of SiO₂ film can be conducted using commonly used RF power, when the post-deposition treatment begins, typically, RF power is increased. In the post-deposition treatment, generally, when increased RF power is applied, the chemical resistance of a horizontal portion of the film becomes higher, e.g., decreasing wet etch rate, because more impurities can be removed from the horizontal portion of the film. However, if RF power becomes too high, the horizontal portion of the film is damaged and its chemical resistance become lower, e.g., increasing wet etch rate. That is, the relationship between RF power (represented by the horizontal axis) and chemical resistance (represented by the vertical axis) can be expressed by a downward curve having a minimum value, which indicates an optimal RF power. Accordingly, optimal RF power can be determined for the preselected pressure (the optimal RF power varies depending on the pressure) through routine experiment in view of this disclosure.

In some embodiments, no gas other than noble gas is introduced to the reaction space in step S2. In some embodiments, hydrogen gas may be introduced additionally or alternatively at similar flow rate in step S2. In some embodiments, no oxygen nor nitrogen gas or no other reactant nor precursor gas is introduced in step S2.

In step S3, the plasma-treated film is subjected to wet etching to achieve TS—SiO. By step S2, impurities are area-selectively removed from the horizontal portion of the film (i.e., the top/bottom portion of the film), and the horizontal portion of the film becomes densified and increases chemical resistance. By subjecting the plasma-treated film to wet etching, the vertical portion of the film (i.e., the sidewall portion of the film) containing more impurities than does the horizontal portion of the film is predominantly etched or removed, forming a top/bottom-thick profile. In some embodiments, step S3 can be conducted under the conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Conditions for Wet etching Etching solution HF 0.05 to 1% (preferably about 0.1% or less) Etching solution 20 to 30° C. (preferably 25° C.) temperature Duration of etching 30 sec to 5 min (preferably 1 to 2 min) Etch rate 1 to 20 nm/min (preferably 10 to 20 nm/min)

For wet etching, any suitable single-wafer type or batch type apparatus including any conventional apparatuses can be used. Also, any suitable solution for wet etching including any conventional solutions can be used. Since the main component of the film is constituted by SiO₂, if a high concentration of HF solution is used for wet etching, wet etch selectivity becomes insufficient. Thus, typically, a low-concentration of HF solution such as about 0.1% solution is used for wet etching.

FIG. 3 is a flowchart illustrating processes of topology-selective film formation according to another embodiment of the present invention. This embodiment represents the sidewall-thick TS—SiO by area-selective incorporation of impurities. In step S4, a SiO film is deposited on a substrate having trenches. The deposition can be done by any suitable method such as PEALD, thermal ALD, cyclic CVD, or PECVD. In step S5, impurities are adsorbed on a surface of the film prior to plasma exposure. Step S5 can be accomplished by exposing the film to a hydrocarbon gas or the like containing impurities such as carbon and/or halogen but containing no silicon, thereby adsorbing the non-silicon gas onto the surface of the film. In some embodiments, step S5 can be conducted under the conditions shown in Table 3 below.

TABLE 3 (numbers are approximate) Conditions for Impurity deposition Non-silicon gas CH₄, C₂H₆, Cl₂, Br₂, CCl₄, Flow rate of non-silicon gas 1 to 100 sccm (preferably 1 to 10 sccm) (continuous) Temperature 50 to 600° C. (preferably 200 to 500° C.) Pressure 100 to 5000 Pa (preferably 100 to 3000 Pa) Duration 1 sec to 30 sec (preferably 0.1 to 5 sec)

In this embodiment, after step S5, plasma treatment is conducted where impurities other than SiO are present on the surface of the film. The plasma treatment can be conducted in a manner substantially similar to step S2 in FIG. 2 (representing a top/bottom-thick TS—SiO by area-selective removal of impurities) under the conditions shown in Table 1. However, in the sidewall-thick TS—SiO by area-selective incorporation of impurities, despite the fact that step S2 can be conducted in a manner substantially similar to step S2 in the top/bottom-thick TS—SiO by area-selective removal of impurities, the functions of step S2 are entirely opposite to those of step S2 of the top/bottom-thick TS—SiO by area-selective removal of impurities. That is, in step S2 of the top/bottom-thick TS—SiO by area-selective removal of impurities (FIG. 2), the impurities are removed predominantly from the horizontal portion of the film, whereas in step S2 of the sidewall-thick TS—SiO by area-selective incorporation of impurities (FIG. 3), the impurities are incorporated predominantly into the horizontal portion of the film.

In step S2, the impurity-adsorbed film is exposed to a noble gas plasma at relatively low pressure and relatively high RF power so that impurities adsorbed on a horizontal portion of the film are predominantly or sufficiently incorporated thereinto as compared with those adsorbed on a vertical portion of the film. Step S4, step S5, and step S2 are continuously conducted without interruption (without breaking a vacuum), or alternatively, step S5 can be conducted in a chamber different from that used for step S4 or by storing the substrate in a different atmosphere containing impurities, and then, the substrate is reloaded to the chamber used for step S4 to conduct step S3 as illustrated in FIG. 3. When step S4 is cyclic deposition, steps S5 and S2 can be conducted after every one cycle of the cyclic deposition (depositing a monolayer) or after every two or more cycles of the cyclic deposition (depositing a laminate of monolayers). However, the thickness of the film obtained in step S4 should not be more than that which ion bombardment by a plasma cannot penetrate in step S2. A set of steps S4, S5, and S2 can be repeated multiple times until a desired thickness of the film is obtained. In some embodiments, the thickness of the deposited film on the top surface is about 3 nm to about 50 nm, typically about 10 nm to about 20 nm, depending on the intended purposes or use of the deposited film.

In step S3, the plasma-treated film is subjected to wet etching to achieve TS—SiO in a manner substantially similar to step S3 shown in FIG. 2 under the conditions shown in Table 2. By step S2, impurities are area-selectively incorporated into the horizontal portion of the film (i.e., the top/bottom portion of the film), and the horizontal portion of the film becomes more vulnerable to ion bombardment and decreases chemical resistance. By subjecting the plasma-treated film to wet etching, the horizontal portion of the film (i.e., the top/bottom portion of the film) containing more impurities than does the vertical portion of the film is predominantly etched or removed, forming a sidewall-thick profile.

FIG. 4 is a flowchart illustrating processes of topology-selective film formation according to another embodiment of the present invention. This embodiment represents another embodiment of the sidewall-thick TS—SiO by area-selective incorporation of impurities. In step S4, a SiO film is deposited on a substrate having trenches in a manner substantially similar to step S4 of FIG. 3. In step S6, a gas containing impurities (e.g., hydrocarbon gas or the like containing impurities such as carbon and/or halogen but containing no silicon) is added to a plasma gas, so that the film is exposed to a plasma containing active species of elements which are incorporated predominantly into the horizontal portion of the film as impurities, resulting in the film having an impurity distribution similar to that of the film obtained as shown in FIG. 3. In some embodiments, step S6 can be conducted under the conditions shown in Table 4 below.

TABLE 4 (numbers are approximate) Conditions for Impurity-containing plasma deposition Substrate temperature 50 to 600° C. (preferably 200 to 500° C.) Pressure 1 to 5000 Pa (preferably 1 to 100 Pa, more preferably 1 to 50 Pa), depending on RF power Noble gas Ar, He Flow rate of noble gas 1 to 100 sccm (preferably 1 to 10 sccm) (continuous) Non-silicon gas CH₄, C₂H₆, Cl₂, Brs, CCl₄ Flow rate of non-silicon 1 to 100 sccm (preferably 1 to 10 sccm) gas (continuous) RF power (13.56 MHz) 10 to 2000 W (preferably 100 to 1000 W, more for a 300-mm wafer preferably 100 to 600 W), depending on the pressure Duration of RF power 0.1 to 10 sec. (preferably 0.2 to 3 sec.), application depending on the thickness of the film Distance between 5 to 20 mm (preferably 10 to 15 mm) electrodes

Step S4 and step S6 are continuously conducted without interruption (without breaking a vacuum). When step S4 is cyclic deposition, step S6 can be conducted after every one cycle of the cyclic deposition (depositing a monolayer) or after every two or more cycles of the cyclic deposition (depositing a laminate of monolayers). A set of steps S4 and S6 can be repeated multiple times until a desired thickness of the film is obtained. In some embodiments, the thickness of the deposited film on the top surface is about 3 nm to about 50 nm, typically about 10 nm to about 20 nm, depending on the intended purposes or use of the deposited film.

In step S3, the plasma-treated film is subjected to wet etching to achieve TS—SiO in a manner substantially similar to step S3 shown in FIG. 3 under the conditions shown in Table 2. As in the process illustrated in FIG. 3, by step S6, impurities are area-selectively incorporated into the horizontal portion of the film (i.e., the top/bottom portion of the film), and the horizontal portion of the film becomes more vulnerable to ion bombardment and decreases chemical resistance. By subjecting the plasma-treated film to wet etching, the horizontal portion of the film (i.e., the top/bottom portion of the film) containing more impurities than does the vertical portion of the film is predominantly etched or removed, forming a sidewall-thick profile.

FIG. 5 illustrates schematic cross-sectional views showing processes of topology-selective film formation of SiO (TS—SiO) according to different embodiments of the present invention ((a) and (b) represent the top/bottom-thick TS—SiO by area-selective removal of impurities, whereas (a) and (c) represent the sidewall-thick TS—SiO by area-selective incorporation of impurities). In FIG. 5, a SiO₂ film 42 is conformally deposited on a substrate 41 having trenches 46, wherein the SiO₂ film 42 is constituted by a horizontal portion (a top portion 45 and a bottom portion 43) and a vertical portion (a sidewall portion 44), which film covers conformally or evenly the entire surface of the substrate 41 with the trenches 46. The SiO₂ film 42 has a substantially geographically uniform distribution of impurities, including substantially no impurities distributed throughout the film.

In the top/bottom-thick TS—SiO by area-selective removal of impurities, the SiO₂ film 42 in (a) contains impurities substantially uniformly distributed throughout the film, and by exposing the film to anisotropic plasma strike (by ion bombardment), the horizontal portion of the film 45, 43 receives more ion bombardment than does the vertical portion of the film 44, thereby dissociating or separating impurities more from the horizontal portion than from the vertical portion and densifying the horizontal portion. As a result, impurities remain more in the vertical portion of the film than in the horizontal portion of the film, i.e., the vertical portion becomes more vulnerable to wet etching than is the horizontal portion. Thus, by subjecting the film having the uneven distribution of impurities, substantially only or predominantly the vertical portion of the film can be removed as illustrated in (b).

In contrast, in the sidewall-thick TS—SiO by area-selective incorporation of impurities, the SiO₂ film 42 in (a) contains impurities substantially uniformly distributed throughout the film including substantially zero or low level of impurities throughout the film, and by adsorbing impurities onto the surface of the vertical and horizontal portions of the film, followed by plasma exposure, or by exposing the vertical and horizontal portions of the film to a plasma containing active species of impurities, wherein the horizontal portion of the film 45, 43 receives more ion bombardment than does the vertical portion of the film 44, thereby incorporating impurities more into the horizontal portion than into the vertical portion. As a result, impurities are introduced more in the horizontal portion of the film than in the vertical portion of the film, i.e., the horizontal portion becomes more vulnerable to wet etching than is the vertical portion. Thus, by subjecting the film having the uneven distribution of impurities, substantially only or predominantly the horizontal portion of the film can be removed as illustrated in (c).

In some embodiments, in the top/bottom-thick TS—SiO by area-selective removal of impurities illustrated in (b) in FIG. 5, a conformality of the final film (a ratio of film thickness at sidewalls (e.g., at a middle point in a cross sectional view) to film thickness at top portions (e.g., at a middle point in a cross sectional view) is about 30% or less including substantially 0% (e.g., about 0%, about 10%, about 20%, about 30%, or any numbers in ranges between any two of the foregoing numbers). In some embodiments, in the sidewall-thick TS—SiO by area-selective incorporation of impurities illustrated in (c) in FIG. 5, the reciprocal of a conformality of the film (a ratio of film thickness at sidewalls, e.g., at a middle point in a cross sectional view, to film thickness at top to film, e.g., at a middle point in a cross sectional view, is about 30% or less including substantially 0%, e.g., about 0%, about 10%, about 20%, about 30%, or any numbers in ranges between any two of the foregoing numbers). In the above, the film thickness at the bottom may vary depending on the aspect ratio of the trench, RF power, the pressure, etc. For example, if the aspect ratio of the trench is high, e.g., 5 to 10, or higher, RF power is relatively low, and/or the pressure is relatively high, the film at the bottom of the trench tends to remain upon wet etching as compared with the film at the top, because sufficient ion bombardment by a plasma may not be able to reach the bottom of the trench.

In the process sequence described in this disclosure, the precursor may be supplied in a pulse using a carrier gas which is continuously supplied. This can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 30. The carrier gas flows out from the bottle 30 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 30, and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B, the carrier gas flows through the gas line with the valve a while bypassing the bottle 30. In the above, valves b, c, d, e, and f are closed.

The precursor may be provided with the aid of a carrier gas. Since ALD is a self-limiting adsorption reaction process, the number of deposited precursor molecules is determined by the number of reactive surface sites and is independent of precursor exposure after saturation, and a supply of the precursor is such that the reactive surface sites are saturated thereby per cycle. A plasma for deposition may be generated in situ, for example, in an ammonia gas that flows continuously throughout the deposition cycle. In other embodiments the plasma may be generated remotely and provided to the reaction chamber.

As mentioned above, each pulse or phase of each deposition cycle is preferably self-limiting. An excess of reactants is supplied in each phase to saturate the susceptible structure surfaces. Surface saturation ensures reactant occupation of all available reactive sites (subject, for example, to physical size or “steric hindrance” restraints) and thus ensures excellent step coverage. In some embodiments the pulse time of one or more of the reactants can be reduced such that complete saturation is not achieved and less than a monolayer is adsorbed on the substrate surface.

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas (and noble gas) and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a dilution gas is introduced into the reaction chamber 3 through a gas line 23. Further, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the processes can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere. In some embodiments, a remote plasma unit can be used for exciting a gas.

In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics, and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.

EXAMPLES Example 1

In this example, the sidewall-thick TS—SiO by area-selective incorporation of impurities was conducted as illustrated in FIG. 4. However, this example was rather an experimental example, since step S6 in FIG. 4 was conducted using polyimide tape (with an acryl adhesive) with which a substrate adhered to a susceptor, which tape was exposed to a plasma and expected to be a source of impurities including carbon (airborne-molecular contaminants, AMC) which was released into the plasma, forming a plasma containing active species of carbon (as opposed to forming a plasma containing active species of impurities by adding a gas containing impurities to a plasma gas). The above step is considered to be functionally equivalent to step S6, wherein both steps produce a plasma containing active species of impurities.

First, a SiO film was formed on a Si substrate (Φ300 mm) having trenches by PEALD, one cycle of which was conducted under the conditions shown in Table 5 (deposition cycle) below using the PEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substrate was stored temporarily in the atmosphere, and then, the substrate was adhered to a susceptor surface of the apparatus using polyimide tape with an acryl adhesive. The substrate was then subjected to post-deposition plasma treatment under the conditions shown in Table 5 below, so that the acryl adhesive was exposed to a plasma, generating active species of carbon in the plasma. Thereafter, the substrate was subjected to wet etching under the conditions shown in Table 5 below.

TABLE 5 (numbers are approximate) Conditions for Deposition Cycle Substrate temperature 300° C. Pressure 400 Pa Precursor Hexachlorodisilane Precursor pulse 1 sec Precursor purge 1 sec Reactant O₂ Flow rate of reactant (continuous) 1 sccm Flow rate of carrier gas (continuous) 2000 sccm Ar Flow rate of dilution gas (continuous) 2000 sccm Ar RF power (13.56 MHz) for a 300-mm wafer 200 W RF power pulse 1 sec Purge 1 sec Number of cycles (thickness of film on top 200 times (20 nm) surface) Step coverage (side/top; side/bottom) 95%; 95% Trench depth/width (nm) 80/200 (AR = about 2.5) Distance between electrodes 12 mm Conditions for Plasma treatment Substrate temperature 300° C. Pressure 100 Pa Noble gas Ar or He Flow rate of noble gas (continuous) 1000 sccm Source of impurities (AMC) Polyimide tape with acryl adhesive RF power (13.56 MHz) for a 300-mm wafer 200 W Duration of RF power application 1 sec Conditions for Wet etching Etching solution 0.5% HF Etching solution temperature 25° C. Duration of etching 1 min

Also, as a comparative example, a SiO film was formed on a Si substrate (Φ300 mm) having trenches by PEALD in a manner substantially similar to that described above, and without conducting plasma treatment (no step S6 was performed), continuously, the substrate was subjected to wet etching in a manner substantially similar to that described above.

The results are shown in FIG. 6. FIG. 6 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of a silicon oxide film as deposited in (a), a silicon oxide film after dHF etching without plasma treatment in (b), and a silicon oxide film after dHF etching upon plasma treatment in (c). As shown in (c) in FIG. 6, when the substrate was exposed to a plasma containing active species of impurities, substantially only or predominantly the top portion of the film was etched, leaving substantially only or predominantly the sidewall portion of the film. In contrast, as shown in (b) in FIG. 6, when the substrate was not exposed to a plasma, substantially only or predominantly the sidewall portion of the film was etched, leaving substantially only or predominantly the top portion of the film. The above appeared to be because impurities contained in the plasma were incorporated substantially only or predominantly into the top portion of the film, rendering the top portion of the film more vulnerable to wet etching than was the sidewall portion of the film.

In (b) in FIG. 6, the top/bottom-thick TS—SiO was achieved without a process of area-selective removal of impurities. This appeared to be because PEALD had anisotropic characteristics and activated the horizontal portion, rather than the vertical portion, of the film, rendering the horizontal portion high quality (high density and/or low impurity concentration), depending on the deposition conditions, etc. By employing the process illustrated in FIG. 2, the quality of the horizontal portion of the film can be further improved, and the wet etch selectivity of the film between the horizontal and vertical portions can be further improved. Further, in the event that the film is deposited by thermal ALD, the film quality is uniform and in principle, there is no difference between the horizontal and vertical portions of the film. In that case, the plasma treatment is required to achieve top/bottom-thick TS—SiO.

In (c) in FIG. 6, the bottom portion of the film was not etched or removed as much as the top portion of the film, despite the fact that both were horizontal portions. It appeared that sufficient ion bombardment by the plasma did not reach the bottom portion because the aspect ratio of the trenches was too high, RF power was low, and/or the pressure was too high. By manipulating these parameters (e.g., changing the aspect ratio to about 2 or less), the bottom portion of the film could be removed or etched to the extent observed in the top portion of the film.

Reference Example 1

In this reference example, consistent with the above in Example 1, it was confirmed that impurities (carbon and nitrogen) were incorporated into a film by plasma treatment at a low pressure, and a portion of the film containing more impurities was more vulnerable to wet etching.

A film (blanket film) was deposited in a manner substantially similar to that in Example 1, and then, the film was exposed to a plasma in a manner substantially similar to that in Example 1 except that the treatment pressure was changed as shown in FIG. 7, followed by wet etching in a manner substantially similar to that in Example 1. FIG. 7 is a graph showing the relationship between treatment pressure [kPa] and wet etch rate (“WERR. Tox”: wet etch rate relative to thermal oxide) of the films. As shown in FIG. 7, when the treatment pressure was 100 Pa (“No. 2”), WERR was very high (i.e., low quality film with low resistance to chemicals), whereas when the treatment pressure was 500 Pa, 2,000 Pa, and 10,000 Pa, WERR was low (i.e., relatively high quality film with relatively high resistance to chemicals), as compared with “Reference” which represents the film as deposited without plasma treatment. When the treatment pressure was as high as 50,000 Pa (“No. 1”), WERR was increased because of insufficient ion bombardment by a plasma.

Also, the films were subjected to composition analysis (atomic %) by X-ray photoelectron spectroscopy (XPS) (analysis was conducted after removing a surface of each film in a depth of 2 nm by sputtering in order to eliminate unwanted contaminations). The results are shown in Table 6 below (“Reference”, “No. 1”, and “No. 2” correspond to “Reference”, “No. 1”, and “No. 2” in FIG. 7, respectively, and “ND” refers to “not detected”). As shown in Table 6, it was confirmed that impurities (carbon and nitrogen) were incorporated into the film by the plasma treatment at a low pressure (“No. 1”). When the treatment pressure was as high as 50,000 Pa (“No. 2”), impurities were no incorporated in the film as with the film without plasma treatment (“Reference”).

TABLE 6 (numbers are approximate) Sample Plasma C Si O N Reference No ND 32.8 67.2 ND No. 1 Yes ND 32.8 67.2 ND No. 2 Yes 4.1 31.3 63.9 0.6 No. 3 Yes 3.4 32.9 62.7 1.1

In the above, No. 3 shows the data of a film obtained in the same manner as in No. 2 except that the SiO film was deposited at a temperature of 300° C. It was confirmed that even when the deposition conditions were changed, the sidewall-thick TS—SiO could be achieved by area-selective incorporation of impurities.

Prophetic Example 1

In this example, the sidewall-thick TS—SiO by area-selective incorporation of impurities is performed as illustrated in FIG. 3. A SiO film is deposited in a manner substantially similar to that in Example 1 as step S4 in FIG. 3. In place of use of polyimide tape with an acryl adhesive in Example 1, upon deposition of the film, without breaking a vacuum, CxHy gas (x and y are integers other than zero) and Ar are introduced to the chamber at about 0.5 slm and about 2 slm, respectively, so as to expose the film to the hydrocarbon gas for about one minute, thereby adsorbing impurities (e.g., carbon) onto a surface of the film. Thereafter, step S2 in FIG. 3 is conducted under conditions similar to those for the plasma treatment in Example 1, followed by wet etching (step S3 in FIG. 3) under the conditions similar to those in Example 1. As a result, the sidewall-thick TS—SiO having a topology similar to that shown in (c) in FIG. 6 is achieved.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We claim:
 1. A method for forming a dielectric film containing a Si—O bond on a step formed on a surface of a substrate, comprising processes of: (i) designing a topology of a final dielectric film containing a Si—O bond formed on the step by preselecting a target portion to be selectively removed with reference to a non-target portion of an initial dielectric film resulting in the final dielectric film, said target portion being a top/bottom portion of the initial dielectric film formed on a top surface and a bottom surface of the step or a sidewall portion of the initial dielectric film formed on a sidewall of the step; (ii) conformally depositing a sublayer of the initial dielectric film on the top surface, the bottom surface, and the sidewall of the step; (iii) relatively increasing an amount of impurities contained in the sublayer of the target portion of the initial dielectric film relative to an amount of impurities contained in the sublayer of the non-target portion of the initial dielectric film to obtain a sublayer of a treated dielectric film; (iv) repeating processes (ii) and (iii) to accumulate each sublayer until a thickness of the accumulated sublayers of the initial dielectric film is greater than a desired thickness of the final dielectric film, thereby obtaining the treated dielectric film and giving the target portion and the non-target portion thereof different chemical resistance properties when subjected to wet etching using dHF; and (v) wet etching the treated dielectric film using dHF to obtain the final dielectric film.
 2. The method according to claim 1, wherein the impurities include carbon and/or halogen.
 3. The method according to claim 1, wherein in process (i), the sidewall portion is preselected as the target portion, and in process (ii), the initial dielectric film is deposited using a silicon-containing precursor further containing carbon and/or halogen, and in process (iii), the amount of impurities contained in the target portion is relatively increased by decreasing the amount of impurities contained in the non-target portion of the initial dielectric film by anisotropic bombardment of a noble gas plasma as a sole plasma excited by applying RF power between two electrodes between which the substrate is placed in parallel to the two electrodes.
 4. The method according to claim 1, wherein in process (i), the top/bottom portion is preselected as the target portion, and in process (iii), the amount of impurities contained in the target portion is relatively increased by increasing the amount of impurities contained in the target portion of the initial dielectric film by (iiia) adsorbing a non-silicon gas containing carbon and/or halogen on the entire exposed surface of the initial dielectric film, and (iiib) subjecting the non-silicon gas-adsorbed surface to anisotropic bombardment of a noble gas plasma as a sole plasma excited by applying RF power between two electrodes between which the substrate is placed in parallel to the two electrodes.
 5. The method according to claim 1, wherein in process (i), the sidewall portion is preselected as the target portion, and in process (iii), the amount of impurities contained in the target portion is relatively increased by increasing the amount of impurities contained in the target portion of the initial dielectric film by (iiic) subjecting the initial dielectric film to anisotropic bombardment of a plasma excited by applying RF power, in the presence of a non-silicon gas containing carbon and/or halogen, between two electrodes between which the substrate is placed in parallel to the two electrodes.
 6. The method according to claim 1, wherein in process (ii), the initial dielectric film is deposited by plasma-enhanced ALD or thermal ALD.
 7. The method according to claim 3, wherein the silicon-containing precursor is selected from the group consisting of Si₂R_(y)Cl_(6-y) wherein y is an integer of 0 to 5, and SiR_(x)Cl_(4-x) wherein R is H or an alkyl group, and x is an integer of 0 to
 3. 8. The method according to claim 3, wherein the RF power is 0.85 W/cm² to 1.41 W/cm² per surface area of the substrate, and is applied under a pressure of 1 to 100 Pa.
 9. The method according to claim 4, wherein the non-silicon gas is selected from the group consisting of hydrocarbon gas, halogen gas, and halogenated gas.
 10. The method according to claim 4, wherein the RF power is 0.85 W/cm² to 1.41 W/cm² per surface area of the substrate, and is applied under a pressure of 1 to 100 Pa.
 11. The method according to claim 5, wherein the non-silicon gas is selected from the group consisting of hydrocarbon gas, halogen gas, and halogenated gas.
 12. The method according to claim 5, wherein the RF power is 0.85 W/cm² to 1.41 W/cm² per surface area of the substrate, and is applied under a pressure of 1 to 100 Pa.
 13. The method according to claim 1, wherein the concentration of HF is approximately 0.1%. 